Liquid ink printers of the type frequently referred to as continuous stream or as drop-on-demand, such as piezoelectric, acoustic, phase change wax-based, or thermal, have at least one printhead from which droplets of ink are directed towards a recording sheet. Within the printhead, the ink is contained in a plurality of channels. Power pulses cause the droplets of ink to be expelled as required from orifices or nozzles at the end of the channels. Continuous ink stream printers are also known.
In a thermal ink-jet printer, the power pulses are usually produced by a thermal transducer component, such as a resistor, each located in a respective one of the channels, which are individually addressable to heat and vaporize ink in the channels. As voltage is applied across a selected resistor, a vapor bubble grows in that particular channel and ink bulges from the channel orifice. At that stage, the bubble begins to collapse. The ink within the channel retracts and separates from the bulging ink thereby forming a droplet moving in a direction away from the channel orifice and towards the recording medium whereupon hitting the recording medium a spot is formed. The channel is then refilled by capillary action, which, in turn, draws ink from a supply container of liquid ink. Operation of a thermal ink-jet printer is described in, for example, U.S. Pat. No. 4,849,774.
The ink-jet printhead may be incorporated into either a carriage-type printer or a page-width type printer. The carriage-type printer typically has a relatively small printhead containing the ink channels and nozzles. The printhead can be sealingly attached to a disposable ink supply cartridge and the combined printhead and cartridge assembly is attached to a carriage which is reciprocated to print one swath of information (equal to the length of a column of nozzles), at a time, on a stationary recording medium, such as paper or a transparency. After the swath is printed, the paper is stepped a distance equal to the height of the printed swath or a portion thereof, so that the next printed swath is contiguous or overlapping therewith. The procedure is repeated until the entire page is printed. In contrast, the page-width printer includes a stationary printhead having a length sufficient to print across the width or length of a sheet of recording medium. The paper is continually moved past the page-width printhead in a direction substantially normal to the printhead length and at a constant or varying speed during the printing process. A page-width ink-jet printer is described, for instance, in U.S. Pat. No. 5,192,959.
A typical ink jet printhead for use in an ink jet printer includes an ink flow directing component or orifice plate, such as an etched silicon substrate containing a linear array of channels open at one end in communication with a common ink reservoir and a logic and thermal transducer component, also known as a heater plate, which includes, for example, a linear array of individual heating elements, usually resistors, monolithically integrated logic drivers, and control circuitry. The orifice plate is aligned with and mated to the heater plate with one resistor aligned with each channel and located at a predetermined distance from the channel open end. The channel open ends serve as the droplet ejectors, expelling channels, or nozzles. Power MOS drivers immediately next to and integrated on the same substrate as the array of resistors are driven by the control circuitry, also integrated on the same substrate, that selectively enable the drivers which apply current pulses to the resistors.
One known method of fabricating thermal ink jet printheads is to form a plurality of the ink flow directing components and a plurality of logic, driver, and thermal transducer components on respective silicon wafers, and then aligning and bonding the wafers together, followed by a process for separating the wafers into a plurality of individual printheads, such as by dicing. The individual printheads are used in one common design of printer in which the printhead is moved periodically across a sheet of paper to form the printed image, much like a typewriter. Individual printheads can also be butted together side by side, placed on a supporting substrate, aligned, and permanently fixed in position to form a large array thermal ink jet printhead or a page width array printhead.
While orifice plates of silicon wafers can provide good printing density and accurate printing of images, silicon is an expensive material and must be etched to create the ink carrying features, such as channels and ink reservoirs. The etching process is a fairly tedious process and is quite costly when considering that the channel plate has no active components but merely provides a physical structure for carrying ink past the heater for ejection from the channels. In addition, etching of a silicon wafer is a complicated process which includes relying on the introduction of chemicals to form the ink carrying features. Consequently, while silicon orifice plates provide meet design requirements, less costly and consistently reproducible orifice plates are desired.
Various liquid ink printheads, including orifice plates, and methods of fabrication therefor are illustrated and described in the following disclosures which may be relevant to certain aspects of the present invention.
In U.S. Pat. No. 4,972,204 to Sexton, an orifice plate for use in ink-jet printing is described. The orifice plate includes a first elongated lamina composed of electroformed metal or metal alloy having tensile or compressive stress condition and a second elongated lamina composed of a metal or metal-alloy electroformed onto the first lamina and having a counterbalancing stress condition.
U.S. Pat. No. 5,218,754, to Rangappan, describes a thermal ink-jet printhead designed to have a length equivalent to the width of a page. A channel plate is made on a single piece of desired length by molding any material that can be molded. Subsequently, the channel plate is hardened to form a rigid structure.
U.S. Pat. No. 5,255,017 to Lam describes a process of forming a mandrel for manufacturing ink-jet orifice plates. The mandrel includes a substrate, a pattern of electrically conductive surfaces on the substrate and an oxide layer on the pattern of conductive surfaces for reducing adhesion of an electroplated film to the pattern of conductive surfaces. The mandrel is used for electroforming an ink-jet orifice plate.
Xerox Disclosure Journal, Vol. 4, No. 2, March/April 1979, entitled "Process For Fabrication of Ink-Jet Orifices" describes a method for forming a large number of closely spaced accurately defined orifices in a metal plate. A pattern of raised, hardened resist posts are developed on a conductive substrate. The area between the posts is filled with metal by electroforming. The electroformed metal is stripped off the conductive substrate to create the orifice plate.
Xerox Disclosure Journal, Vol. 6, No. 3, May/June 1981, entitled "Bi-Laminar Ink-Jet Aperture Plate Formation", describes nickel electroforming of ink-jet aperture plates. The ink-jet aperture plate is strengthened by placing another layer over the original layer while preventing metal deposition immediately adjacent the previously formed apertures.